Almost all human beings suffer from caries for a variety of reasons such as over-consumption of sweet foodstuffs and poor dental care. Many also suffer from hypersensitive tooth necks particularly the middle aged population. It is important for the dental industry to restore, reduce and prevent these problems. However, despite new technologies, the human population is still suffering from caries and sensitive teeth.
It has been found that the hard tissues of human teeth have many very small micro-channels defined therein. The channels penetrated tooth's major hard components such as the enamel, dentine and root cement and constitute a continuous fluid system that extends from the inside and out to the surface of the tooth. The enamel may be described as an ectodermal tissue composed of rod-shaped structural units that have a diameter of about 4-5 micrometers. The enamel includes large hydroxyapatite crystals embedded in an organic matrix of non-collagenous proteins and lipids. Mesodermal dentine also contains hydroxyapatite crystals but the crystals are smaller and the organic matrix consists of collage and water.
The microchannels are used as a vehicle for providing a means for communication between the interior of the pulp tissue of the tooth and the exterior saliva throughout the life of the tooth. Among other things, the channels often serve as transport ways for ions and molecules through the dental hard tissues to the pulp and out therefrom. The average diameter of these microchannels is about 5-20 nanometers in the enamel and about 1-3 micrometers in the dentine. The microchannels are filled with a native biohydrogel of a fibrous protein origin. The native biohydrogel is a natural polymeric material that can swell in aqueous biological fluids and retain a significant amount of fluid.
Whenever the pH falls below 5.5 in the ambient oral environment, some of the hydroxyapatite crystals may dissolve in the microchannels thus widening their lumens. Destructive metabolites and toxins from microorganisms can then easily penetrate the enlarged microchannels. The caries process and bacterial metabolites and toxins may inflame the underlying pulp tissue which may increase the sensitivity of the tooth. The microorganisms may also cause inflammatory reactions in the underlying pulp tissue.
Hypersensitivity of the tooth may arise due to excessive movement of the fluid in the native biohydrogel within the microchannels. The amount of movement of the fluid is partially dependent upon the viscosity of the biohydrogel. However, the native biohydrogel may adversely change its viscosity depending upon such stimuli as the temperature, pH value, ion concentration and electrical potential in the microchannels.
There is a need to make the viscosity of the natural hydrogel more stable and possibly to increase the viscosity thereof to reduce the sometimes painful effect of excessive movement of the fluid that causes hypersensitivity. Any substance used for this purpose should not be allergenic, carcinogenic, mutagenic or toxic. Additionally, the substance should be tasteless, colorless, and not smell and have a viscosity that is suitable for the application on the tooth surface without unnecessarily prolonging the application time. It is also important that the substance does not discolor the dentine over time.
The substance should also be compatible with the native biohydrogel and be able to withstand acid-hydrolytic degradation and biodegradation caused by acids and enzymes present in the oral cavity. The substance should also be able to absorb ions present in the human saliva and to take part in the natural obliteration of the channels with increased age.
Many polymeric hydrogels have been tested in the past. For example, polymeric hydrogels based on polyacrylic acids have a dark color that often tends to darken the color of the dentine. Similarly, salts based on hafnium, titanium and zirconium also have a dark color that may discolor the dentine. Synthetic hydrogels, such as calcium alginate hydrogels, tend to degrade by the microorganisms in the oral cavity. Chitosan hydrogels are often resistant to enzymatic and hydrolytic degradation but the hydrogels are often too fragile and are easily ruptured by mechanical forces. Chitosan hydrogels also suffer from a low water binding capacity and have a low cohesion strength in a gel matrix combination with the native bichydrogel. These drawbacks have reduced the clinical use of chitosan hydrogels.
There is a clinical need to prevent the destructive microorganisms from destroying the microchannels and their native biohydrogel while allowing the natural diffusion of ions and molecules. There is also a need to reduce the fluid flow within the microchannels, to reduce demineralization caused by foreign acids and to increase re-mineralization by, for example, calcium phosphates and fluoride.
The present invention is a method for treating a tooth having a tooth surface with a plurality of tubules defined therein. The tooth is treated with a polymeric hydrogel formed by a polyphosphazene substance and a metal salt. The polyphosphazene substance is first applied to the tooth surface and then the metal salt is applied thereto. The polyphosphazene substance is reacted with the metal salt to form a polymeric hydrogel inside the tubules.